Automatic Speech Recognition (ASR) technologies enable microphone-equipped computing devices to interpret speech and thereby provide an alternative to conventional human-to-computer input devices such as keyboards or keypads. Many telecommunications devices are equipped with ASR technology to detect the presence of discrete speech such as a spoken nametag or control vocabulary like numerals, keywords, or commands. For example, ASR can match a spoken command word with a corresponding command stored in memory of the telecommunication device to carry out some action, like dialing a telephone number. Also, an ASR system is typically programmed with predefined acceptable vocabulary that the system expects to hear from a user at any given time, known as in-vocabulary speech. For example, during a voice dialing mode, the ASR system may expect to hear keypad vocabulary such as “Zero” through “Nine,” “Pound,” and “Star,” as well as ubiquitous command vocabulary such as “Help,” “Cancel,” and “Goodbye.”
ASR systems use microphones. And different microphones have a wide range of frequency response and sensitivity characteristics. The frequency response and particular sensitivity performance depends upon the microphone manufacturer, but significant differences exist even between seemingly identical microphones made by the same manufacturer. Due to existing tolerances in microphone production methods, differences exist between what would appear to be the same microphone. To compensate for the different microphones, ASR systems are programmed to process a wide spectrum of signals from microphones having a great variety of sensitivities and frequencies. For instance, while the ASR system may receive a signal from a particular microphone having a narrow frequency range and/or limited sensitivity, the ASR system will nevertheless operate as though the microphone provided a wide frequency range and great sensitivity. The ASR system operates in this manner because the system is unaware of the characteristics of the particular microphone. In short, compensating for various microphones involves an ASR system searching for sounds outside the performance characteristics of a microphone. As a result, the ASR system engages in needless processing that consumes energy and decreases response time and speech recognition accuracy.